Previously, it has been known to use aspen particles, chips, shavings etc as a litter for animals. However, this material has traditionally often been composed of all aspen, without other woods or substances introduced. Further, these 100% aspen litters were composed of essentially all portions of the tree, including the bark. Although such "litters" are suitable for use as horticultural mulch, the inclusion of the tree bark causes an appearance which is considered to be unsightly when the material is used as a litter, and particularly a litter for small animals, such as those which would be kept in a person's home, or for use in places of display, such as pet shops.
Other litter compositions including alfalfa or related forage crops are known for their utility as animal litters which effectively absorb animal waste materials and neutralize associated unpleasant odors. For example, alfalfa has been pelletized with starch, as disclosed in U.S. Pat. No. 3,923,005. Such pellets overcome the disadvantage of earlier pelletized alfalfa by reducing the problem of disintegration of the pellets, which caused the litter material to cling to the animal's feet.
A further improvement of alfalfa pellets was disclosed in U.S. Pat. No. 3,941,090 which discusses pelletizing cedar in combination with alfalfa binders.
U.S. Pat. No. 4,788,936 discloses pelleted bedding for livestock, which bedding includes 4 to 45% by volume of aspen bark, with the balance being a combination of sawdust, ground wood chips and ground lumber. U.S. Pat. No. 5,271,355 discloses absorbent material formed of pelleted poplar wood, preferably aspen, including the tree bark, and peat. Optionally, the material may also include cedar wood.
All of the above references involve absorbent materials that are completely pelletized. However, the process of pelletization is complex and thus expensive. Aspen is especially difficult to pelletize, because it is a hard, dry wood which exacts a toll on the extruding equipment used for the pelletizing process, by causing greater amounts of wear on the equipment parts, resulting in the expense of frequent maintenance and replacement.